The deposition of tungsten films using chemical vapor deposition (CVD) techniques is an integral part of many semiconductor fabrication processes. The tungsten films may be used to produce low resistance electrical connections in the form of horizontal interconnects, vias between adjacent metal layers, and contacts between a first metal layer and the devices on a substrate. In a conventional tungsten deposition process on a semiconductor wafer, the wafer is heated to the process temperature in a vacuum chamber, and then a very thin portion of tungsten film, which serves as a seed or nucleation layer, is deposited. Thereafter, the remainder of the tungsten film (the bulk layer) is deposited on the nucleation layer. The bulk layer is generally deposited more rapidly than the nucleation layer, but cannot be produced easily and reliably without first forming the nucleation layer.
Increasingly thin tungsten electrical connects having very low resistance will enable smaller critical dimension devices. Although CVD and other methods are able to deposit nucleation layers, their ability to provide nucleation layers for the deposition of low resistivity tungsten in small critical dimension features is limited. Void-free fill in aggressive features is problematic using conventional CVD tungsten deposition techniques.